The invention is related to a device for charging and discharging printing media in printing presses and copiers, particularly of printing media during the passage along the transfer paths of printing presses and copiers.
Printing media such as paper sheets, films or the like are electrically discharged during the passage along the transfer paths of printing presses and copiers. In order to prevent the printed paper sheets or film from sticking to one another in the output bin or sticking to sufficiently electrically conductive components on the transfer path, these electrical charges must be discharged. It is known practice to use passive discharging devices such as carbon fiber or stainless steel brushes, or active discharging devices such as corona-discharging devices that are operated by AC high voltage and which have corona wires and/or ionization tips, for this purpose. With such devices, the ions generated by the electric fields between the corona wires or ionization tips and the electrical charges to be discharged are attracted and their effect is offset in this manner. The efficiency of the discharging depends on the environmental conditions.
Such types of discharging devices are known from the U.S. Pat. No. 5,890,046, whereby the high voltage AC field between two corona-discharging devices to each of which a corona wire has been applied and the printing media is passed through between these corona-discharging devices. In the above-mentioned patent, one of the corona-discharging devices is mounted on a rotating distribution roller, whereas the second corona-discharging device is fixed in place.
In the German Published Application DE 34 27 919 A1, a corona-discharging device is illustrated that has a grid-type guide opposite the printing media that is being passed through. However, this grid-type guide concerns an opposite electrode to the inner-lying corona wire. In addition, the electrode, along with a continuous belt conveying the printing media, is passed through the opposite electrode and the corona wire.
The U.S. Pat. No. 5,552,873 shows a guiding device within a combined corona-charging/discharging device, which has bridging members that bridge the interior of the discharging device. The bridging members are arranged in the middle area of the guiding device so that they are spaced further apart from one another than in the areas toward the outside. Furthermore, the bridging members have a different slant with respect to the transport direction of printed material via the discharging device.
The German Patent No. 435686 shows a comparable guiding device combined in corona charging/discharging devices, in which the border of the guiding device is arranged in a manner to prevent a disturbance between the charging device and the discharging device.
The U.S. Pat. No. 5,130,752 shows similar bridging members of a guiding device within a corona-discharging device, which has additional tilts along the standard direction of movement of printing media that are intended to prevent an edge of the printing media from being caught in the path along the bridging members.
One problem with such corona charging/discharging devices is the change of the electrical field between two corona-discharging devices, when printing media or no printing media is found between the corona wires. Likewise, there is a dependency on the electrical resistance of such printing media. In the border area of the gap between the corona wires, in which the passage gap is no longer covered by the printing media, flashovers can occur due to the considerable difference between the electrical resistance and the associated greater electric field strength outside the area covered by the printing media. These types of flashovers generate a disturbing noise for the control and lead to damage of the electronics in the worst-case scenario.
It is thus the purpose of this invention to provide a device for the charging and discharging of printing media in printing presses and copiers, in which the danger of flashovers is reduced. This is accomplished with the device according to the invention for charging and discharging printing media in printing presses and copiers.
In a particularly advantageous embodiment of the device, the slim bridging members of the guiding device extend at an angle a to the transport direction of the printing media over the entire width of the passage gap. Advantageously, the width of the passage gap basically corresponds to the width B of the largest printing media format, which is discharged in the middle area of the corona-discharging device. In another advantageous embodiment of the device according to the invention, the bridging members and, where necessary, the frames of the guiding device, are composed of an electrical non-conducting material. As a result, the influence of the guiding device on the electrical field between the corona wires is minimized. This supports the slim configuration of the bridging members, which bridge the passage gap and thus covers the smallest surface possible of the passage gap and thus also leads to the smallest distortion possible of the electrical field between the corona wires.
Advantageously, the device is formed in two parts on both sides of the transport path of printing media with at least a first corona wire and a first guiding device on the first side and at least a second corona wire and a second guiding device on the second side.
In another particular embodiment of the device according to the invention, there is a smaller distance between the bridging members of the guiding device at the border of the passage gap than between the bridging members in the middle area of the passage run. In this case, the border of the guiding gap is distinguished in that, for all of the printing formats to be guided, the outside edges of the printing media are located within the border area. The result of the smaller distance between the bridging members is that only a small area of the passage gap is covered, material is saved, and on the other side in the border area, it can be guaranteed with great reliability that if the printing media is dog-eared, such sections are reliably guided through the more closely positioned bridging members from the passage gap into the transfer path.
In another advantageous form of the invention, the bridging members of the guiding device at the border of the passage gap are slanted at a greater angle to the transport direction of the passage gap than in the middle area of the passage gap. As a result, the guiding functions of the bridging members can be advantageously supported. In the border area, the guiding device should, in principle, be reliably guided over the passage gap without creased or bent corners. This functionality increases with increasing angles to the transport direction up to a position of the bridging members in which they are 45xc2x0 to the transport direction. However, in the middle area, it is the task of the bridging members to reliably guide the leading edges of printing media over the passage gap. This function is improved with smaller angles of the bridging members to the transport direction, since this reduces the probability that an incoming leading edge is caught on a bridging member. Thus, it is an advantage if the tilt of the bridging members increases from the inside to the outside.
In a particularly advantageous further development, the bridging members at the border of the passage gap have an angle of essentially 45xc2x0 to the transport direction of the printing media. In another advantageous further development, the bridging members in the middle area of the passage gap have an angle of essentially 15xc2x0 to the transport direction of the printing media. Particularly advantageously, the bridging members between the middle area and the border of the passage gap have an angle between essentially 15xc2x0 to 45xc2x0 to the transport direction of the printing media, whereby the angle increases toward the outside.
Advantageously, this type of guiding device is such that the bridging members on the side turned towards the printing media have been rounded off. As a result, the guiding function of the device is supported, since the bearing surface of printing media to the guiding device is reduced. In addition, edges are avoided, since otherwise there is always a possibility that the printing media will be tilted in the transport path.
In another particularly advantageous embodiment of the device according to the invention, the guiding device has entry tilts that are tilted toward the standard direction of movement of the printing media toward the transport direction and incoming printing media tends to be directed toward the middle area of the passage gap. Advantageously, one entry tilt is located at the entrance and the other one at the exit of the passage gap.
In another embodiment of the device according to the invention, the guiding device has one guide finger each in the middle area of the slim side of the guiding device on the side turned toward the printing media. The guide fingers cover the side-by-side corona wires in the border area of the passage gap. As a result, the straight path from one corona wire to another for the corona ions in the border area is interrupted. With the presence of printing media in the middle area of the passage gap, the ion flow in the border area increases, as a result of which the danger of flashovers in this area is increased. Due to the guide fingers, however, the corona ions in this area are to a large extent intercepted, particularly those in the direct connecting line between two corona wires, and thus do not contribute to a further ionization of the air in the border area of the passage gap. As a result, the danger of flashovers is reduced.
In another particularly advantageous further development of the invention is the distance of the ends of the guide fingers from each other and thus the adaptation of the length of the guide fingers to the format of the smallest printing media to be passed through, particularly in such a way that the smallest printing media to be passed through, which runs in the middle through the guiding device, covers the ends of both guide fingers. As a result, by using the smallest format possible, the danger of a flashover is still reduced, and, on the other hand, the covering of the corona wires with printing media of a larger format is minimized in the border area, and thus an optimal discharging of the border area of printing media can also be achieved.
Advantageously, each guide finger of a guiding device according to the invention has an entry tilt, which is slanted in the standard direction of the printing media toward the transport direction. Thus the guiding function of the device according to the invention can be further supported.
In an advantageous embodiment of the invention, the guiding device has devices on the side turned toward the printing media that can be used to attach the guiding device to the discharging device. In this way, the assembly costs are reduced, and other attachment mechanisms are used.
The guiding devices suggested according to the invention for guiding printing media and their components, which are equipped with discharging and charging equipment, may be used in all sheet-processing equipment. Furthermore, a new application is created for all devices that deal with printing media, in which printing media are guided along a transport path.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.